The use of fibrous structures in absorbent articles such as diapers or feminine hygienic articles is well known in the art. Fibrous structures may be either consolidated, bonded webs, such as nonwoven webs, but can also be unbonded structures, often made of natural fibers such as cellulose fibers or chemically modified cellulose fibers.
Unbonded fibrous structures can for example be used as absorbent cores, wherein the fibers are typically mixed with superabsorbent gelling materials, such as superabsorbent polymer particles. Moreover, such unbonded fibrous structures can be used in so-called liquid acquisition systems overlaying the absorbent core.
With the processes used today for high speed manufacture of fibrous webs for absorbent articles, it is difficult to make unbonded fibrous webs having a relatively low basis weight, such as basis weights below 120 g/m2 as such fibrous webs typically suffer from poor homogeneity, resulting in holes in the web and low web integrity. When used in absorbent articles, holes lead to reduced integrity of the fibrous structure, which can reduce the liquid handling performance of absorbent articles.
EP-A-0 252 650, published on Jan. 13, 1988, discloses processes for making individualized, stiffened fibers. The fibers may be directly deposited on a foraminous forming wire in a manner similar to conventional pulp sheeting processes and formed into pulp sheets. Pulp sheets may be undensified or compacted. In one embodiment the individualized, stiffened fibres are combined with conventional fibres to be made into a densified pulp sheet for subsequent defibration and formation into absorbent pads. The incorporation of the conventional fibers eases dry compression of the pulp sheet into a densified form.
Whereas mixtures of fibres, such as mixtures of individualized, stiffened fibers combined with conventional fibers, can be processed into absorbent pads using the methods of the prior art, it would be desirable to provide more flexible processes in which pulp sheets can be transformed into various absorbent pads, the pads having different compositions, different profiles, different densities etc.
Thus the present invention provides a method wherein roughly graded material of first fibrous sheets having certain composition can be mixed with second material(s) after defiberising and directly prior to forming the fibrous structure or pad.